The present invention relates to an optical head, a method for manufacturing an optical head, and an optical disk apparatus.
Conventionally, the optical heads (namely, optical pick up) are known in the art, for instance, from JP-A-64-46242 and JP-A-64-43822.
The optical head described in JP-A-64-46242 is so constructed that the surface emitting laser and the photodetector are formed on the same substrate, the glass plates are stacked, or laminated on this substrate, and the focusing grating coupler (hologram lens) is fabricated on the surface of this glass plate.
On the other hand, the optical head described in JP-A-64-43822 is so arranged that the above-described optical head disclosed in JP-A-64-46242 is employed as the optical head main body, and this optical head main body is mounted on the flying slider.
In the optical head disclosed in JP-A-64-46242, the focusing grating coupler is utilized. In case of such a focusing grating coupler, chromatic aberration is large when the wavelength of the light from the light source is varied due to temperature variations and the like. Although this prior art describes that there is no change in the wavelengths when the surface emitting laser is employed, there is adverse influence since the wavelength is changed by the temperatures, as apparent from the publication "SURFACE EMITTING LASER" written by Iga, FIG. 12, page 8, vol. 60, No. 1, APPLIED PHYSICS, 1991. Accordingly, this prior art owns such a problem that no solution means is taken to the wavelength variation.
Furthermore, as to the optical head described in JP-A-64-46242, the optical path to the optical disk is inclined in order to separate the optical path for the laser light emitted from the surface emitting laser to the optical disk, from the optical path for the light returned from the optical disk to the photodetector. When the optical path is inclined, there is a problem that aberration and also asymmetrical strength distributions may easily occur, resulting in a large spot size of the laser light. It should be noted that the applications of the SCOOP structure have been proposed in this prior art, taking account of such a problem caused by the inclined optical path. However, since only differences in reflectivities of the medium can be detected in case of the SCOOP structure, there are drawbacks that neither the tracking signal, nor the opto-magnetic signal can be detected.
On the other hand, in the optical head described in JP-A-64-43822, since the optical head is mounted on the flying slider separately manufactured, it is very difficult to adjust the slider surface and the optical head within the normal focal depth from 2 micrometers to 3 micrometers. If the automatic focusing control would be performed, then this focal depth adjustment would not be required. However, since JP-A-64-43822 has such an object that this automatic focusing control is not performed, the above-explained difficult focal depth adjustment must be carried out.
It should also be noted that JP-A-64-43822 never discloses a method for manufacturing an optical head with employment of a surface emitting laser, and also an optical disk apparatus suitable for a flying type optical head.